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effects on pH

Posted: Tue Jan 21, 2020 10:31 am
by Katie Bart 1I
Why do conjugate bases/acids and group 1/2 cations not affect pH?

Re: effects on pH

Posted: Tue Jan 21, 2020 10:50 am
by Veronica_Lubera_2A
I think you're mentioning solubility rules so you don't include groups 1 and 2 in the reaction because they don't affect pH (totally dissolve in water and are present on both sides of the reaction so you can cancel them out). Example is NaOH and also salts like NaCl don't affect pH. Conjugate bases/acids though of relevant molecules will affect pH.

Re: effects on pH

Posted: Tue Jan 21, 2020 11:44 am
by Kaylee Clarke 1G
Group 1/2 cations are considered spectator ions and therefore are insignificant.

Re: effects on pH

Posted: Tue Jan 21, 2020 12:41 pm
by Brian_Ho_2B
The general rule is that the stronger an acid/base is, the weaker its conjugate. The weaker an acid/base is, the stronger its conjugate. Group 1/2 cations (with the exception to Magnesium, but that's a topic for a more advanced chemistry class) do not affect pH because they are mostly stable and those ions are not strong enough to break the O-H bonds in water to act as a base. However, transition metal cations that are highly charged (eg. +3) are very polarizing and can affect pH.

Re: effects on pH

Posted: Tue Jan 21, 2020 12:54 pm
by pmokh14B
Because those conjugates are more stable than their respective acids/bases, so they stay in solution rather than reacting to form hydronium or hydroxide.

Re: effects on pH

Posted: Wed Jan 22, 2020 1:19 am
by Jainam Shah 4I
Group 1 and group 2 cations are typically cations from a strong acid or base. For example the Na+ of NaOH and K+ from KOH. If you look at the reaction for both of these in the presence of water you would see that since these are strong bases they full disassociate. The cation thus has no point or ability to participate in a reverse reaction and is basically an extremely weak conjugate acid that cannot contribute to the pH. Like the others said it is also a spectator ion on both sides of the reaction so it doesn't change the concentration.

Re: effects on pH

Posted: Wed Jan 22, 2020 1:35 am
by ThomasNguyen_Dis1H
Conjugate acids or conjugate bases of strong acids are very weak. This is due to the fact that Kw=Ka*Kb. Since Kw is a constant, when one of the K increases the other must decrease. So take for example HCl, it will have a very high Ka value since it dissociates completely which means the Kb will be a very small value which represents the conjugate base of Cl-.

Re: effects on pH

Posted: Wed Jan 22, 2020 3:09 pm
by Ruth Glauber 1C
They're considered spectator ions and insignificant!